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Hydroformylation of Higher Olefins in Supercritical Carbon Dioxide with HRh(CO)[P(3,5-(CF3)2-C6H3)3]3 Timothy Davis and Can Erkey* Environmental Engineering Program, Department of Chemical Engineering, University of Connecticut, Storrs, Connecticut 06269-3222
A fluorinated analogue of the hydroformylation catalyst, HRh(CO)(PPh3)3 was synthesized for hydroformylation of olefins in supercritical carbon dioxide (scCO2). The catalyst, HRh(CO)[P(3,5(CF3)2C6H3)3]3, was found to be an extremely active catalyst in scCO2 for hydroformylation of 1-octene with maximum TOFs around 15 000 h-1 at a relatively mild temperature of 65 °C. The very high activity results from the low basicity of the ligand. The kinetics of hydroformylation of 1-octene in scCO2 with the catalyst was investigated. The results were successfully interpreted using the generally accepted catalytic cycle in the literature based on a dissociative mechanism. The reaction is nearly first order with respect to H2, which suggests that oxidative addition of hydrogen to an acyl intermediate is the rate-determining step in scCO2 at the low phosphine concentrations employed. The commonly observed decrease in reaction rate with increasing phosphine concentration with HRh(CO)(PPh3)3 in conventional solvents was not observed due to the low basicity of the ligand. 1. Introduction Over 6 million tons of aldehydes per year are produced by homogeneous catalytic hydroformylation and used as feedstock for production of a wide variety of chemicals such as alcohols, diols, carboxylic acids, acroleins, and acetals.1 This reaction involves the addition of carbon monoxide and hydrogen across a C-C double bond. The catalysts employed are of the form HxMy(CO)zLn; the two transition metals utilized are rhodium and cobalt and the most commonly utilized ligands are phosphines (PR3 where R ) C6H5 or n-C4H9). Production of C4 aldehydes from hydroformylation of propene is dominated by rhodium-based catalysts whereas higher aldehydes are produced mainly by cobalt catalysts. In hydroformylation of higher olefins, one of the major issues in switching to 1000 times more active Rh-based catalysts is the difficulty of the separation of products and the catalyst. This is illustrated in Figure 1 , which shows the two industrial processes for propene hydroformylation that employ Rh-based catalysts.2 In the UCC process, propene, a H2/CO mixture, and a high-boiling aldehyde condensation products solution that contains the dissolved catalyst is fed to a reactor. The liquid effluent stream from the reactor is subjected to a complex catalyst recovery scheme consisting of a separator, a pressure letdown valve, a flash evaporator, and two distillation columns in series. The second distillation column operates at subatmospheric pressures around 130 °C. The high boiling points of aldehydes beyond C6 make such an operation impractical, even under reduced pressure due to thermal stability considerations for the catalyst. In the more elegant RCH/RP process, propene and a H2/CO mixture are fed to a CSTR that contains an aqueous solution with a water-soluble catalyst. The effluent from the reactor is passed through a phase separator. The aqueous solution is recycled back to the reactor and the crude aldehydes are sent to a distillation column. The process is utilized for production of C4 and C5 aldehydes; however, application of this concept to higher olefin production is
Figure 1. Industrial processes for rhodium-catalyzed hydroformylation of propene.
highly unlikely due to the extremely low solubilities of higher olefins in water. An alternative may be to utilize supercritical carbon dioxide (scCO2) as the solvent for hydroformylation of higher olefins where the catalyst can be separated from the reaction mixture and recycled by temperature/ pressure tuning. Homogeneous catalysis in supercritical fluids (SCFs) is a rapidly growing field due to favorable properties of SCFs as reaction solvents.3,4 Over the past
10.1021/ie000274v CCC: $19.00 © 2000 American Chemical Society Published on Web 09/09/2000
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Figure 2. Schematic diagram of experimental setup.
couple of years, quite a few studies have been conducted on rhodium-catalyzed higher olefin hydroformylation in scCO2. These started with the pioneering efforts of Leitner’s group who synthesized perfluoroalkyl-substituted arylphosphines and aryl phosphites.5,6 The rhodium complexes of these ligands were found to exhibit high solubility in scCO2 and could catalyze the hydroformylation of higher olefins. Subsequently, Palo and Erkey reported the synthesis and use of RhCl(CO)[P(pCF3C6H4)3]2 and HRh(CO)[P(p-CF3C6H4)3]3 as hydroformylation catalysts in scCO2.7-9 These catalysts exhibited solubilities in the reaction mixture of at least 5.5 × 10-3 mol dm-3 (T ) 343 K, P ) 273 atm) and 7.6 × 10-3 mol dm-3 (T ) 323 K, P ) 273 atm), respectively, indicating that small trifluoromethyl substituents have a dramatic effect on the scCO2 solubilities of rhodium/ phosphine complexes. Recently, Palo and Erkey investigated the effect of ligand modification by fluorous groups on homogeneous hydroformylation of 1-octene in scCO2 at 50 °C and 273 atm.10 The activity of the rhodium complex (formed in situ from Rh(CO)2(acac) and L) increased with decreasing basicity of the phosphine according to the series P[3,5-(CF3)2C6H3]3 > P(4-CF3C6H4)3 ≈ P(3-CF3C6H4)3 > P(4-CF3OC6H4)3 > P[4-F(CF2)4(CH2)3C6H4]3. The ability of oxygen and methylene groups to insulate against the electronwithdrawing effects of the fluoroalkyl moieties could be observed for phosphines P(4-CF3OC6H4)3 and P[4-F(CF2)4(CH2)3C6H4]3, where significant decreases in the IR stretching frequency of metal carbonyls, ν(CO), for the rhodium complexes were accompanied by 50 and 70% decreases in activity, respectively. While these spacers are effective insulators, they actually decrease the catalytic activity relative to “noninsulated” arylphosphines. The very high hydroformylation activity obtained with the catalyst system Rh(CO)2(acac)/P[3,5(CF3)2C6H3]3 prompted us to investigate the kinetics of hydroformylation of 1-octene using HRh(CO)[P(3,5(CF3)2C6H3)3]3, 1. The initial TOFs using this catalyst are around 15 000 mol of aldehyde/mol of rhodium h-1 at 65 °C and 273 atm, a level suitable for large-scale industrial production. In this paper, we report on the synthesis and characterization of 1 and on our investigation of the kinetics of hydroformylation of 1-octene in scCO2 using this catalyst. Our objectives are 3-fold:
1. To provide a rate expression that can be used to design reactors to assess the commercial viability of a scCO2-based hydroformylation process. 2. To determine if the kinetics in scCO2 are consistent with the generally accepted catalytic cycle for hydroformylation of olefins in organic solvents. 3. To elucidate the effects of ligand modification by fluorous groups on the kinetics. 2. Experimental Section Tris(3,5-bis-trifluoromethylphenyl)phosphine was synthesized from 3,5-bis-triflouromethyl, 1-bromobenzene, and phosphorus trichloride through a lithiation reaction. In a three-necked round-bottom flask, 6 g of 3,5-bistriflouromethyl, 1-bromobenzene, and 50 mL of diethyl ether were mixed at room temperature. The flask was put in an ice bath and flushed with nitrogen. Then, 12.84 mL of n-butyllithium (1 M solution in hexane) was added dropwise with an addition funnel. The solution turned red immediately. After 10 min, 25 mL of ether and 0.59 mL of phosphorus trichloride (PCl3) were mixed and added dropwise to the solution through an addition funnel over a period of 30 min. Subsequently, the ice bath was removed and the reaction was allowed to proceed for 3 h. A 20-mL solution of ammonium chloride in water (10 wt %) was slowly injected into the flask under ice. The water layer was removed using a separatory funnel and the ether layer was washed twice with water. The ether was then evaporated and the product distilled. A yellowish-white crystalline product was collected in the condenser. Yield: 53%. 1H NMR (400 MHz CDCl3, 30 °C, CHCl3): δ 7.72 d, 7.97 s ppm. 31P{1H} NMR (400 MHz CDCl , 30 °C, P(O)Ph ): δ 3 3 -4.41 ppm. Next, 1.2 g of the phosphine and 0.129 g of Rh(CO)2acac were placed inside the high-pressure reactor shown in Figure 2. A 50% mixture of CO and H2 was charged to a pressure of 20 bar and the reactor was heated to 50 °C. Carbon dioxide was pumped in until a pressure of 160 atm was achieved. The initial color in the reactor was red, but as time progressed, the color turned yellow. After 1 h, the heater was turned off and the vessel was allowed to cool. The CO2 was slowly vented and the products were collected and washed with
Ind. Eng. Chem. Res., Vol. 39, No. 10, 2000 3673 Table 1. Summary of Conditions for Hydroformylation Experiments in ScCO2 run no.
T (°C)
[octene]0 (M)
[H2]0 (M)
[CO]0 (M)
[catalyst]0 (mM)
P/[Rh]
n:iso ratio
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
50 50 50 50 50 50 50 50 50 50 50 45 40 50 50 50
0.97 0.51 0.25 1.03 1.00 0.97 1.00 1.00 1.00 1.02 1.01 1.03 0.98 1.02 0.99 0.99
1.09 1.18 1.23 2.15 1.62 0.54 1.08 1.08 1.08 1.08 1.08 1.09 1.09 1.09 1.09 1.09
1.09 1.18 1.23 1.08 1.08 1.09 2.16 1.62 0.65 2.15 2.15 1.09 1.09 1.09 1.09 1.09
0.432 0.432 0.432 0.432 0.432 0.432 0.432 0.432 0.432 0.865 1.30 0.432 0.432 0.432 0.432 0.432
3 3 3 3 3 3 3 3 3 3 3 3 3 20 40 100
2.64 2.51 2.59 2.85 2.28 2.48 2.15 2.32 3.65 2.32 2.55 2.62 2.68 3.60 3.74 4.11
chloroform. Yield: 61%. FTIR (ATR, solid): ν(CO) ) 1963 cm-1, ν(RhH) ) 2033 cm-1. 1H NMR (400 MHz CDCl3, 30 °C, CHCl3): δ 7.72d, 7.97s, -10.18q ppm. 31P{1H} NMR (400 MHz CDCl3, 30 °C, P(O)Ph3): δ 44.03d ppm. Calcd for C73H28OP3F54Rh: C, 40.92; H, 1.32. Found C, 39.77; H, 1.29. All kinetic experiments were conducted batchwise in a high-pressure, custom-manufactured, 54-cm3 stainless steel reactor equipped with a high-pressure sampling system, as shown in Figure 2. The reactor was fitted with two sapphire windows for viewing the contents in the reactor (Sapphire Engineering, Inc), poly-etherether-ketone O-rings (Valco Instruments, Inc.), T-type thermocouple assembly (Omega Engineering, DP41-TCMDSS), pressure transducer (Omega Engineering, PX01K1-5KGV), vent line, and rupture disk assembly (Autoclave Engineers). For each experiment, a catalystfilled ampule sealed under vacuum, a magnetic stir bar, and freshly distilled 1-octene were placed in the reactor, which was then flushed with N2 in a glovebox and sealed. The reactor was then placed on a magnetic stir plate and heated to appropriate temperatures by a circulating heater (Haake FJ) via a machined internal heating coil. The reactor was charged with the desired amounts of CO and H2 from gas cylinders and then pressurized with CO2 from a syringe pump (ISCO, 100D) equipped with a cooling jacket. The ampule shattered upon the initial pressurization of the reactor with CO, and the elapsed time from the introduction of CO until the obtaining of a homogeneous mixture was [4-ClC6H4]3P > [4-FC6H4]3P > [4-HC6H4]3P > [4-OCH3C6H4]3P . [4-N(CH3)2 C6H4]3P). The alkyl intermediate, VIII, became the more dominant species as the basicity of the ligand decreased. This was attributed to a shift in the rate-determining step from dissociation of CO from I to a step after the formation of VIII for 4-sub-
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Table 2. Comparison of Rate Expressions for Hydroformylation of Olefinic Substrates with HRh(CO)(PPh3)3 ref.
substrate
solvent
T (°C)
PH2 (bar)
PCO (bar)
[substrate] (M)
[catalyst] (mM)
rate expression 0.05
20
1-propene
toluene
90-110
1-45
1-25
0.1-1.0
1-4
15
1-decene
benzene
50-70
6-30
2-30
0.2-2.5
1.0
k[H2]
[cat][sub]0.6
0.1
[CO] [PPh3]0.7 k[H2]1.5[CO][cat]1.2[sub] (1 + KB[CO])3(1 + Ks[sub])
22
vinyl acetate
ethanol
50-70
3.45-34.46
13.79-34.46
0.49-2.89
0.337-1
19
allyl alcohol
ethanol
60-80
13.79-39.01
3.53-41.3
0.4-6.6
1-4
k[H2][CO][cat][sub] (1 + KB[CO])3(1 + Ks[sub])2 k[H2]1.523[CO][cat][sub] (1 + KB[CO])3(1 + Ks[sub])2
18
1-hexene
ethanol
30-50
6.19-17.15
0.75-17.15
0.2-1.56
0.33-1.2
23
ethene
toluene
60-100
4.14-27.56
4.14-27.56
4.14-27.56
0.5-4
k[H2][CO][cat][sub] (1 + KB[CO])2.5(1 + Ks[sub])2.1 k[H2]1.5[CO][cat][sub] (1 + KB[CO])2(1 + Ks[sub])2
17
16
1-dodecene
ethene
toluene
tetraglyme
50-70
80-110
6.8-17.0
2.87-7.47
1.7-20.4
0.081-5.62
0.18-2.2
0.072-0.378
1-8
0.058-0.932
k[H2][CO][cat][sub] (1 + KB[CO])2(1 + Ks[sub]) pC2H4 k1 [PPh3] pCO [PPh3] 1 + K1 + K2 pCO [PPh3]
24
1-octene
scCO2
50
5.0-70.0
5.0-60.0
0.04-0.96
0.63-2.5
k[H2]0.48[cat]0.84[sub]0.5 1 + KB[CO]2.2
Figure 3. Comparison of experimental and predicted reaction rates.
Figure 4. Hydroformylation of 1-octene using 1: effect of catalyst concentration {T ) 50 °C, P ) 273 atm, [1-octene]0 ) 1.00-1.02 mol dm-3, [H2]0 ) 1.08 mol dm-3 [CO]0 ) 2.15 mol dm-3}.
stituted ligands less basic than PPh3. The weakening of the Rh carbonyl bond due to the decreasing basicity of the ligand evidence was provided as evidence. The second possibility is that either oxidative addition of H2 to IX or olefin addition to II/III and/or insertion (VIII to IX) is the rate-determining step. The mechanistic models based on either of these rate-determining steps can predict the inhibiting effect of [CO] on the rate of hydroformylation.15,16 When [PPh3] is low, oxidative addition is rate determining, whereas at high [PPh3], the rate-determining step shifts to olefin addition and/ or insertion. This shift is accompanied by a change of
reaction order with respect to H2 from 1 to zero. The third possibility is that increasing the [CO] in the system also results in an increase of the concentration of coordinatively saturated acyl intermediate, XI, which cannot oxidatively add hydrogen, thus diminishing the rate. The phosphine concentrations used in development of the rate expression in scCO2 are very low. On the basis of the studies in the literature, one would expect the reaction to be first order H2, which would be accompanied by an inhibiting effect of increasing [CO]. Furthermore, the phosphine used in this study is even
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Figure 5. Hydroformylation of 1-octene using 1: effect of initial 1-octene concentration {T ) 50 °C, P ) 273 atm, [H2]0 ) 1.091.23 mol dm-3, [CO]0 ) 1.09-1.23 mol dm-3, [1] ) 0.432 × 10-3 mol dm-3}.
Figure 6. Hydroformylation of 1-octene using 1: effect of initial hydrogen concentration {T ) 50 °C, P ) 273 atm, [1-octene]0 ) 0.98-1.03 mol dm-3, [CO]0 ) 1.08-1.09 mol dm-3, [1] ) 0.432 × 10-3 mol dm-3}.
Figure 7. Hydroformylation of 1-octene using 1: effect of initial carbon monoxide concentration {T ) 50 °C, P ) 273 atm, [1-octene]0 ) 1.00 mol dm-3, [H2]0 ) 1.08 mol dm-3, [1] ) 0.432 × 10-3 mol dm-3}.
less basic than P(4-CF3C6H4)3 studied by Moser et al.,13 so the alkyl intermediate is most likely the dominant species under hydroformylation conditions in scCO2. This would result in a rate-determining step after the
formation of VII, which may also be oxidative addition of H2. This is in accordance with the fact that decreasing basicity of the ligand should result in a decrease in the ease of activation of hydrogen.12 Therefore, the reaction nearly being first order with respect to H2 is in agreement with the studies in the literature and shows that oxidative addition of H2 is also the rate-determining step in scCO2. The formation of the intermediate XI in scCO2 may also be contributing to a certain extent on the inhibiting effect of [CO]. In conventional organic solvents such as toluene at 323 K, the [CO] in solution at a partial pressure of 10 atm CO is around 0.05 M based on the Henry’s Law constant given by Bhanage et al.17 On the other hand, the [CO] in scCO2 in the experiments conducted in this study are about 20 times higher, which may favor the formation of XI. The selectivity decreased from 3.65 to 2.15 as [CO]0 increased from 0.65 to 2.16 mol L-1. This phenomena is also commonly observed in organic solvents and can be attributed to the increase in the molar ratio of II to III when [CO] decreases. Because the CO ligand is much less sterically demanding than the phosphine, selectivity decreases. Effect of 1-Octene Concentration. Initial 1-octene concentration was varied from 0.25 to 1 M and the order with respect to 1-octene was 0.4. The studies in the literature for hydroformylation in organic solvents indicate a positive dependence on olefin concentration until a critical substrate/catalyst ratio is reached, after which the dependence becomes zero or negative.16-19 This phenomena has been termed saturation kinetics or substrate inhibition and is usually attributed to a shift in the rate-determining step. It has been proposed that, at the saturation limit, the rate-determining step is oxidative addition of hydrogen to IX, while at low olefin concentrations, the rate-determining step is olefin addition to II. The fractional order observed in this study suggests that, under the conditions studied, the system may be operating close to an intermediate regime. [1-octene]0 did not significantly affect the final n:iso ratio. Effect of Catalyst Concentration. The nearly firstorder dependency of the rate on catalyst concentration is in agreement with the studies in the literature. Selectivity increased from 2.15 to 2.55 as 1 increased from 0.43 to 1.29 mM. The increase can be attributed to the increase in [II]/[III] by increasing the free phosphine concentration in the system. Effect of Phosphine Concentration. It has generally been observed that increasing the [PPh3] increases the rate up to a certain limit beyond which further increases in [PPh3] result in a decrease in rate and an increase in selectivity. At high [PPh3], the reaction order with respect to PPh3 was found to be -0.7 by d’Oro et al. for hydroformylation of propene20 and between -0.41 and -0.49 by Kiss et al. for hyfroformylation of ethene.16 It has been suggested that the kinetic behavior of the phosphine dependency reflected the trapping of a 16electron intermediate.16 Along similar lines, Moser et al. showed that, at high [PPh3], the dominant species were I and XIII and the concentration of the inactive species XIII increased with increasing P/Rh ratio, thus causing a decrease in reaction rate.13 A similar reduction in rate of reaction was recently observed by Koch and Leitner6 in rhodium-catalyzed hydroformylation of olefins in scCO2 (catalyst prepared in situ from Rh(cod)hfac and P[4-F(CF2)6(CH2)2C6H4]3). This phosphine is
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Figure 8. Catalytic rate cycle for the hydroformylation of olefins using HRh(CO)L3.
Figure 9. Hydroformylation of 1-octene using 1: effect of phosphine concentration {T ) 50 °C, P ) 273 atm, [1-octene]0 ) 0.971.02 mol dm-3, [H2]0 ) [CO]0 ) 1.09 mol dm-3}.
electronically similar to PPh3 due to the methylene spacers. The TON decreased from 280 to 40 as the P/[Rh] ratio increased from 4 to 13. In this study, the data from the experiments conducted at different phosphine concentrations are given in Figure 9 where, surprisingly, no decrease in activity was observed with increasing phosphine concentration. This result suggests that the formation of the dimer and/or trapping of a 16-electron intermediate by the excess phosphine
Figure 10. Hydroformylation of 1-octene using 1: effect of phosphine concentration on selectivity {T ) 50 °C, P ) 273 atm, [l-octene]0 ) 0.97-1.02 mol dm-3, [H2]0 ) [CO]0 ) 1.09 mol dm-3}.
is prevented by the low basicity of the ligand. As explained in the previous sections, increasing the [PPh3] shifts the rate-determining step in organic solvents from oxidative addition to olefin addition and/or insertion. The nearly identical concentration profiles at different P/[Rh] investigated in this study suggests that such a shift does not occur in scCO2. As shown in Figure 10, as the P/[Rh] ratio increased from 3 to 100, the n:iso ratio increased from 2.64 to 4.11.
Ind. Eng. Chem. Res., Vol. 39, No. 10, 2000 3677
is very interesting and can be attributed to the low basicity of the ligand. Acknowledgment Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the ACS, for partial support of this research (ACS-PRF 32299-ACl). We are also grateful for financial support from the Honor’s Program at the University of Connecticut. Literature Cited (1) Parshall, G. W.; Ittel, S. D. Homogeneous Catalysis: The Applications and Chemistry of Catalysis by Soluble Transition Metal Complexes, 2nd ed.; John Wiley & Sons: New York, 1992. Figure 11. Hydroformylation of 1-octene using 1: effect of temperature {P ) 273 atm, [1-octene]0 ) 0.97-1.03 mol dm-3, [H2]0 ) [CO]0 ) 1.09 mol dm-3, [1] ) 0.432 × 10-3 mol dm-3.
(2) Frohning, C. D.; Kohlpaintner, C. W. Hydroformylation (Oxo Synthesis, Roelen Reaction). In Applied Homogeneous Catalysis with Organometallic Compounds; Cornils, B., and Herrmann, W. A., Eds.; VCH: Weinheim, 1996; p 29. (3) Morgenstern, D. A.; LeLacheur, R. M.; Morita, D. K.; Borkowsky, S. L.; Feng, S.; Brown, G. H.; Luan, L.; Gross, M. F.; Burk, M. J.; Tumas, W. Supercritical Carbon Dioxide as a Substitute Solvent for Chemical Synthesis and Catalysis. In Green Chemistry: Designing Chemistry for the Environment; Anastas, P. T., Williamson, T. C., Eds.; American Chemical Society: Washington, DC, 1996. (4) Jessop, P. G.; Ikariya, T.; Noyori, R. Homogeneous Catalysis in Supercritical Fluids. Chem. Rev. 1999, 99, 475. (5) Kainz, S.; Koch, D.; Baumann, W.; Leitner, W. Perfluoroalkyl-Substituted Arylphosphanes as Ligands for Homogeneous Catalysis in Supercritical Carbon Dioxide. Angew. Chem., Int. Ed. Engl. 1997, 36, 1628. (6) Koch, D.; Leitner, W. Rhodium-Catalyzed Hydroformylation in Supercritical Carbon Dioxide. J. Am. Chem. Soc. 1998, 120, 13398.
Figure 12. Temperature dependence of the rate constant.
Such trends have also been observed in hydroformylation in conventional solvents and can be attributed to the increase in [II]/[III]. Effect of Temperature. The reaction was also studied at different temperatures. The data are provided in Figure 11. The reaction rate constant was extracted from data at each temperature by assuming that the reaction order with respect to each reactant and the KB did not change with temperature. The good agreement between model (solid lines) and experimental data shows that the assumption is justified. As shown in Figure 12, the rate constants at each temperature were fitted to an Arrhenius-type equation. The activation energy was determined as 22.7 kcal/mol, which compares well with 19.1 kcal/mol for ethene hydroformylation16 with Rh/PPh3, 20.6 for propene hydroformylation20 with Rh/PPh3, and 20.0 kcal/mol for ethene hydroformylation21 with Rh/P(CH2CH2(CF2)5CF3)3. 4. Conclusions The data coupled with mechanistic studies in the literature on hydroformylation of olefins in conventional solvents suggest that the rate-determining step for hydroformylation of 1-octene in scCO2 with 1 is oxidative addition of hydrogen. The lack of a decrease in the rate of reaction with increasing phosphine concentration
(7) Palo, D. R.; Erkey, C. Homogeneous Catalytic Hydroformylation of 1-Octene in Supercritical Carbon Dioxide Using a Novel Rhodium Catalyst with Fluorinated Arylphosphine Ligands. Ind. Eng. Chem. Res. 1998, 37, 4203. (8) Palo, D. R.; Erkey, C. Homogeneous Hydroformylation of 1-Octene in Supercritical Carbon Dioxide with [RhH(CO)(P(pCF3C6H4)3)3]. Ind. Eng. Chem. Res. 1999, 38, 2163. (9) Erkey, C.; Palo, D. R. Rhodium Catalyzed Homogeneous Hydroformylation of Unsaturated Compounds in Supercritical Carbon Dioxide. In Reaction Engineering for Pollution Prevention; Abraham, M., Hesketh, R. P., Eds.; Elsevier: Amsterdam, 1999. (10) Palo, D. R.; Erkey, C. Effect of Ligand Modification on Rhodium-Catalysed Homogeneous Hydroformylation in Supercritical Carbon Dioxide. Organometallics 2000, 19, 81. (11) Evans, D.; Osborn, J. A.; Wilkinson, G. Hydroformylation of Alkenes by Use of Rhodium Complex Catalysts. J. Chem. Soc. A 1968, 3133. (12) Brown, C. K.; Wilkinson, G. Homogeneous Hydroformylation of Alkenes with Hydridocarbonyltris(triphenylphosphine) Rhodium(I) as Catalyst. J. Chem. Soc. A 1970, 2753. (13) Moser, W. R.; Papile, C. J.; Brannon, D. A.; Duwell, R. A. The Mechanism of Phosphine-Modified Rhodium Catalyzed Hydroformylation Studied by CIR-FTIR. J. Mol. Catal. 1987, 41, 271. (14) Bianchini, C.; Lee, H. M.; Meli, A.; Vizza, F. In Situ HighPressure 31P{1H} NMR Studies of the Hydroformylation of 1-Hexene by RhH(CO)(PPh3)3. Organometallics 2000, 19(5), 849-853. (15) Divekar, S. S.; Deshpande, R. M.; Chaudhari, R. V. Kinetics of Hydroformylation of 1-Decene Using Homogeneous HRh(CO)(PPh3)3 Catalyst: A Molecular Level Approach. Catal. Lett. 1993, 21, 191. (16) Kiss, G.; Mozelski, E. J.; Nadler, K. C.; VanDriessche, E.; DeRoover, C. Hydroformylation of Ethene with Triphenylphosphine Modified Rhodium Catalyst: Kinetic and Mechanistic Studies. J. Mol. Catal. A 1999, 138, 155.
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(17) Bhanage, B. M.; Divekar, S. S.; Desphande, R. M.; Chaudhari, R. V. Kinetics of Hydroformylation of 1-Dodecene Using Homogeneous HRh(CO)(PPh3)3 Catalyst. J. Mol. Catal. A 1997, 115, 247. (18) Deshpande, R. M.; Chaudhari, R. V. Kinetics of Hydroformylation of 1-Hexene Using Homogeneous HRh(CO)(PPh3)3 Complex Catalyst. Ind. Eng. Chem. Res. 1988, 27, 1996. (19) Deshpande, R. M.; Chaudhari, R. V. Hydroformylation of Allyl Alcohol Using Homogeneous HRh(CO)(PPh3)3 Catalyst: A Kinetic Study. J. Catal. 1989, 115, 326. (20) d’Oro, P. C.; Raimondo, L.; Pagani, G.; Montrasi, G.; Gregorio, G.; Andreetta, A. Chim. Ind. 1980, 62, 572. (21) Horvath, I. T.; Kiss, G.; Cook, R. A.; Bond, J. E.; Stevens, P. A.; Rabai, J.; Mozeleski, E. J. Molecular Engineering in Homogeneous Catalysis: One-Phase Catalysis Coupled with Biphase Catalyst Separation. The Fluorous-Soluble HRh(CO){P[CH2CH2(CF2)5CF3]3}3 Hydroformylation System. J. Am. Chem. Soc. 1998, 120, 3133.
(22) Deshpande, R. M.; Chaudhari, R. V. Hydroformylation of Vinyl Acetate Using Homogeneous HRh(CO)(PPh3)3 Catalyst: A Kinetic Study. J. Mol. Catal. 1989, 57, 177. (23) Deshpande, R. M.; Bhanage, B. M.; Divekar, S. S.; Kanagasabapathy, S.; Chaudhari, R. V. Kinetics of Hydroformylation of Ethylene in a Homogeneous Medium: Comparison in Organic and Aqueous Systems. Ind. Eng. Chem. Res. 1998, 37, 2391. (24) Palo, D. R.; Erkey, C. Kinetics of the Homogeneous Catalytic Hydroformylation of 1-Octene in Supercritical Carbon Dioxide. Ind. Eng. Chem. Res. 1999, 38, 3786.
Received for review February 28, 2000 Revised manuscript received June 22, 2000 Accepted July 13, 2000 IE000274V
